The present invention relates to a bone anchoring element for insertion into a bone or a vertebra that has a deflectable screw for dynamic stabilization. Further the present invention also relates to a stabilization device for such a bone anchoring element.
Conventional bone anchoring elements for the fixation of bone fractures or the stabilization of spinal columns typically consist of at least two screws anchored in a bone and/or a vertebra that are connected by a rigid plate or a rod. Because the screws are fixed relative to each other, the conventional bone anchoring elements are rigid and do not allow the bone and/or the vertebra to move.
In instances where dynamic stabilization is desired, the bone and/or the vertebra need to be stabilized such that the bone and/or the vertebra are capable of performing controlled, limited motion relative to each other. Dynamic stabilization may be obtained by using a flexible element instead of a rigid plate or rod to connect the screws, such as described in, for example, European Patent EP 0 669 109 B1 and U.S. Patent Publication No. 2003/0109880 A1. Because the screws are coupled by a flexible element, movement of one of the screws is transferred to the other screw through the flexible element. Due to the permanent cyclical partial load on the bone anchoring element, this transfer of movement can cause the screw to become loose in the bone and/or the vertebra, which can lead to separation of the screw from the bone and/or the vertebra.
Consequently, there is a need to uncouple the motion of the bone and/or the vertebra from the rod or the plate so that the bone anchoring elements remain securely anchored in the bone and/or the vertebra for the life of the patient. Moreover, there is a need to be able to optimally position the bone anchoring element relative to a rod or a plate connecting multiple bone anchoring elements.
One known way to achieve these needs is though a conventional polyaxial bone screw. One example of a polyaxial bone screw is described in U.S. Pat. No. 5,474,555. The polyaxial bone screw comprises a screw and a receiving member that is connecting to a rod. The screw is anchored in a bone and is connected to the receiving member such that the screw can swivel or pivot relative to the receiving member. The polyaxial bone screw that is described, however, does not allow for mutual stabilization of the bone and controlled partial motion thereof.
It is therefore desirable to develop a bone anchoring element for anchoring in a bone and/or a vertebra wherein the bone anchoring element allows controlled partial motion of the bone and/or vertebra that is to be stabilized, secure attachment to the bone and/or vertebra, and optimal positioning.
The foregoing paragraphs have been provided by way of general introduction and are not intended to limit the scope of the claims. The presently preferred embodiments together with further advantages will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.